In bowling, it is desirable to have the ball hook somewhat as it is rolling down the alley, as the bowling ball will then tend to knock down a greater number of pins as compared with a ball following a straight path. To make a ball hook, it is desirable to apply upward force or "lift" to the ball as it is being released, by initially withdrawing the thumb from the thumb hole, and completing the release of the ball using the two fingers.
Most good bowlers use finger inserts or grips in the finger holes to increase the friction between the fingers and the bowling ball during the critical instant as the ball is being released.
Now, in most bowling balls, the finger holes are 31/32 inch in diameter and about 11/8 or 11/4 inches deep. Finger inserts normally are available in about ten different sizes increasing in increments of one-thirty-second inch, in the inner diameter of the insert, from about 19/32 inch to about 7/8 inch (28/32 inch). The demand for all of these different sizes, possibly for more than one brand of insert, means that bowling equipment shops must maintain an extensive inventory of inserts, and often do not buy sufficient quantities of any one insert from their suppliers to get a quantity discount.
It is further noted that at least certain types of inserts do not provide the finger gripping action or frictional engagement which would be desirable.
Accordingly, principal objects of the present invention are (1) to provide an insert having improved gripping engagement with the fingers, and (2) to combine two sizes of inserts in a single insert with accurate fit for each size, and without any adverse effects being noticeable to the user.